1. Field of the Invention
The invention relates to a process for producing a multi-layer lacquer coating with a mechanically stable quick-drying clear-lacquer coating based on systems curable by radiation.
2. Description of Related Art
Coatings as applied in the series production of automobiles nowadays mostly consist of a surface lacquer of basecoat and clear lacquer which is applied to bodywork that has been electrophoretically primed and coated with filler. In this process basecoat and clear lacquer are preferably applied wet-on-wet, i.e. after a flash-off period optionally subject to heating. After subsequent application of a clear lacquer the basecoat is stoved together with this lacquer, as described for example in EP-A-38 127 and EP-A-402 772. In this connection suitable clear lacquers are described, for example, in EP-A-38 127 and EP-A-184 761. The stoving process in industrial production lacquering requires long drying phases, and naturally a certain time passes before the lacquer is no longer tacky, so that special measures have to be taken in order to avoid incorporating dust in the surface.
Both in the case of the use of one-component (1C) and also of two-component (2C) clear lacquers the lacquering process is associated with emissions of environmentally harmful solvents or dissociation products of the crosslinking reaction. In the case for example of isocyanate-crosslinking 2C clear lacquers, e.g. according to DE-OS 33 22 037 or DE-PS 36 00 425, recycling of overspray is by its nature not possible.
In JP-A-6213 2570 clear UV lacquers are described which serve to protect electrical instruments used in domestic appliances and in the automobile industry. They are applied in a thin film; multiple precoating does not take place.
In EP-A-0 118 705 and GB-A-2 226 566 UV-curable layers are described for protecting automobile underbodies from the impact of stones. The layers are applied with a thickness of up to 1500 .mu.m. They are formulated so as to be soft and elastic and are not capable of being ground.
In EP-A-0 247 563 coatings are described which by way of surface lacquer have a coating which in addition to an isocyanate-hydroxyl-group crosslinking reaction is also subjected to crosslinking by UV radiation. The overspray accruing during application of the coating agent can in view of the chemical reaction no longer be subjected to recycling.